This invention relates to a device for breaking a tablet, and in particular to a device for measuring the force required to break the tablet.
Tablets have long been convenient dosage forms for a variety of materials, such as medicaments, vitamins, foods and detergents. It is important that each tablet be of the same weight and content of active material within close limits in order to ensure a constant dosage. In addition, each tablet must have sufficient hardness to withstand the shock of handling, packing and shipping. This latter requirement led to the development of hardness testers, such as the Strong-Cobb, Stokes-Monsanto, Pfizer and Heberlein hardness testers. These well-known devices are based on the same principle of operation, namely, diametral crushing of a tablet.
In the Strong-Cobb tester, the force required to break a tablet across the diameter is produced by a manually or pressure operated pump. As the pressure increases, a plunger is forced against a tablet set on edge. A dial indicator records the final breaking force.
The Pfizer hardness tester operates on the same mechanical principle as ordinary pliers. As the tablet is crushed in the jaws of the device, the force is recorded on a dial indicator. The dial indicator remains at the reading where the tablet breaks. It returns to zero when a reset button is pressed.
The Stokes-Monsanto tester consists of a barrel containing a compressible spring held between two plungers. The lower plunger is brought into contact with the tablet. The upper plunger is forced against the spring by a threaded bolt and the force is transmitted against the tablet. As the spring is compressed, a pointer rides along a gauge in the barrel and indicates the pressure at which the tablet fractures.
The Heberlein tester operates in a horizontal position. A moving anvil presses the tablet against a stationary anvil. As force is applied to the edge of the tablet, a pendulum swings away from its normal position. Its movement is followed by a pointer moving along a scale indicator. When the tablet breaks, the pendulum swings back to its original position while the pointer indicates the scale reading in both kilograms and in Strong-Cobb units.
Compressed tablets are frequently orally administered to animals and humans. While tablets for animal and human consumption are normally available in unit dosages, it is frequently necessary to reduce the dose, such as by breaking the tablet in half, and consuming only half the tablet. Traditionally, tablets have been broken by hand. This can be accomplished by breaking the tablet between the second and third fingers of one hand while the thumb is used as a fulcrum or by using the index fingers of both hands while the thumbs serve as a fulcrum.
It is important for the tablet formulator to have some indication of the force that will be required to break the tablet by hand. Tablets can then be formulated for specific uses. For example, persons with decreased strength in the hands or those suffering from diseases, such as arthritis, or those with handicaps, such as amputees, may encounter considerable difficulty in breaking tablets. The tablet formulator can provide such individuals with tablets that require a relatively low breaking force. When the tablets are manufactured, the manufacturer must be able to determine the breaking strength of the tablets for quality control purposes.
Thus, there exists a need in the art for a tablet breaking device capable of measuring the force required to break the tablet. The measured force should be representative of the force that will be required for a human to break a similar tablet using one of the traditional manual methods. The tablets should break evenly in the device without crushing. Ideally, the device should be of relatively simple construction, easy to manufacture and simple to operate.